It is proposed to synthesize hemes labeled in specifically chosen positions with deuterium, tritium, or carbon-13, and to approach these compounds by two different routes. One approach will involve regioselective modification of existing commercially available hemes (e.g. protoporphyrin-IX or hemin), whereas the alternative route will involve total synthesis from monopyrroles. After reconstitution into myoglobin, hemoglobin, cytochromes, and peroxidases, NMR spectroscopy will be used to establish unique assignments of heme-associated resonances in these proteins. The effect of peripheral substituents on key properties such as heme electronic structure will then be characterized using the chemical shift spread, for example, of the synthetically associated methyl groups. From this it is intended to obtain a detailed understanding of the way in which the nature of heme changes with protein contacts in heme proteins, and therefore of structure-activity relationships in this important series of metalloproteins. The synthetic deuterium labeled hemes and heme proteins will also be used for assignment of peaks in infrared and resonance Raman spectra of these compounds.